System interconnecting facility

1. A system interconnecting facility connected to a power system, the system interconnecting facility comprising: a plurality of power converters connected to the power system; a plurality of transformers provided between the power system and the power converters; a plurality of switches provided between the transformers and the power converters; and a controller that controls opening and closing of the switches, wherein the controller outputs, to the switches, respective open and close commands so that a number of closed switches is out of a closed switch number range that is the range within which a harmonic voltage of the system interconnecting facility increases, based on a harmonic voltage containing rate characteristic that is a relationship between the number of closed switches and a harmonic voltage containing rate of the system interconnecting facility.

2. The system interconnecting facility according to claim 1 , wherein the controller outputs, to the switches, the open and close commands that achieve the number of closed switches which causes the harmonic voltage containing rate to be equal to or smaller than a predetermined threshold.

3. The system interconnecting facility according to claim 2 , wherein the controller comprises: a switch status collecting unit that collects open and close status information of each of the switches; a closed switch number collecting unit that collects the number of closed switches from the open and close status information; a voltage acquiring unit that acquires a measured voltage from a voltage sensor which measures a voltage containing a fundamental wave voltage and an odd-order harmonic voltage; and an arithmetic processing unit that calculates the harmonic voltage containing rate from the acquired fundamental wave voltage and odd-order harmonic voltage, and acquires the harmonic voltage containing rate characteristic from the number of closed switches and the calculated harmonic voltage containing rate.

4. The system interconnecting facility according to claim 3 , wherein: the arithmetic processing unit acquires the harmonic voltage containing rate characteristic when the harmonic voltage containing rate decreases; and the controller changes the closed switch number range based on the harmonic voltage containing rate characteristic acquired when the harmonic voltage containing rate decreases.

5. The system interconnecting facility according to claim 1 , wherein the controller comprises a load power command unit that outputs, to a load within the system interconnecting facility, a command to consume power.

6. The system interconnecting facility according to claim 1 , comprising a plurality of sets of the switches and the power converters, each of the sets containing a switch and a converter connected in series, wherein, the controller sequentially executes a control action for each of the sets, the control action including outputting a command to close the switch and outputting a command to switch the converter connected in series to the closed switch.

7. The system interconnecting facility according to claim 1 , wherein the controller comprises a database for a dead band of each of the power converters, and the controller outputs, to a power converter, a charging and discharging command value that causes a total output of the power converters to become close to zero based on the dead band.

8. The system interconnecting facility according to claim 7 , wherein: the power converter comprises a receiving unit that receives a harmonic reducing command value to cause output power to be zero regardless of the dead band; and the controller comprises a transmitting unit that transmits, together with an activation signal to the power converter, the harmonic decreasing command value.